Amplifier coupling



Jan. 20, 1931. H. P. DONLE 1,789,673

AMPLIFIER COUPLING Filed March 30, 1926 6 INVENTOR HaroIdRDonIe,

' 5 Q Y T'NEY Patented Jan. 20, 1931 UNITED STATES PATENT OFFICE HAROLDPOTTER DONLE, 0F MERIDEN, CONNECTICUT, ASSIGNOR, *BY MESNE ASSIGN- MENTS, TO RADIO INVENTIONS, INC., A CORPORATION OF NEW YORK AMPLIFIERCOUPLING Application filed March 30, 1926. Serial No. 98,451.

My invention relates to signal receiving apparatus and apparatus for anysystems employing so called vacuum tube amplifiers.

There are three methods of coupling commonly used in the art, viz:transformer, resistance and impedance. Transformer coupling has longbeen recognized as most efficient from the view of volume amplification,but it frequently gives rise to troublesome distortion and the outputvaries considerably with the intensity of the applied signal. Resistancecoupling is inefficient as to volume and it sometimes gives a chokingefi'ect especially on heavy signals.

Impedance coupling is a partially effective attempt to combine the goodqualities of the transformer coupling and the resistance coupling.Generally it is more efiicient than transformer coupling for high inputand more efficient than the resistance type of coupling but it does notgive the general volume amplification per tube of the transformercoupling and has some disadvantages in common with resistance coupling.

The object of this invention is to obtain a highly eflicient couplingwithout the disadvantages above pointed out.

Fig. 1 shows diagrammatically parts of a typical system embodying myinvention.

Fig. 2 is a side view and section of the preferred form of couplingdevice.

Fig. 3 is a plan View of the same.

The coupling device is made as a unit for connection in any system or itmay be built in to a set. In any event it will consist of two inductancecoils L and L on a common core 5 and a condenser C. One coil isconnected between the B battery and the plate P of the first tube andthe other coil is connected between the filament F and the grid G of thenext tube. The condenser is inserted between the plate of the first tubeand the grid of the second. The device may have suitable terminals tofacilitate the various connections in any suitable manner.

The core may be of any suitable construction and has a closed magneticcircuit with out any magnetic shield or leakage tongue between thebranches on which the coils are mounted. It has been found most convenacritical value.

ient and desirable to'mount the coils on opponot less than'.()01microfarads and preferably of about .25 microfarads although this is notThe condenser may be located between the coils.

The absolute values of the inductances depend upon circumstances and theVarious circuit constants. The coils and condenser are preferably housedin a case 6 which may have an insulating top 7 with terminals P, B, F

and G for connection to the corresponding elements.

Such a combination gives excellent results at all usual values of inputsignals and is particularly desirable on loud signals because it doesnot load up or choke as do all of the other systems of amplifiercoupling. When properly designed the device is comparatively free fromfeed-back and oscillation and in fact it is possible with this system ofcoupling to use several stages without difliculty and to give perfectquality of signal reproduction under conditions where choke orresistance coupling would be almost completely inoperative.

The construction is not only more simple and efficient mechanically butalso electrically. There is a certain amount of transfer of energy fromone coil to the other through the core and the balance through thecondenser. The amount of transfer of energy from one coil to the othercan be determined by the reluctance of the iron core.

I claim 1. An audio frequency amplifier having vacuum tubes with acoupling device be-- tween them comprising an inductance inserted in theplate-cathode circuit of one tube, an inductance inserted in thegridcathode circuit of the following tube, a closed magnetic core commonto both inductances for producing a substantial mutual inductancebetween said circuits, and a condenser connected directly between theplate and grid terminals of said inductances, the second mentionedinductance being connected at one end between the condenser and the gridof the second tube and at its other end to the filament of the secondtube whereby a substantial capacity coupling is produced, saidinductances having low ohmic resistance and impedance sufliciently highto insure an eflicient transfer of energy from one inductance to theother at audio frequencies.

2. An audio frequency amplifier having vacuum tubes with a couplingdevice between them comprising the combination of a transformer having asingle closed circuited magnetic core with primary and secondarywindings arranged in mutually inductive relation, said windings havinglow resistance and substantial impedance at audio frequencies, acondenser connected between the high voltage ends of'said windings andto the plate and grid of the respective tubes and without substantialinpedance, whereby part of the energy is transferred electro-staticallythru the capacity and a part electromagnetically by the windings and thecore.

HAROLD P. DONLE.

